World map drawn in the 15th century from Claudius Ptolemy's data. The map extends through 180 degrees of longitude eastwards from the prime meridian in the Canary Islands to eastern Asia, but not including the coastline of China. The effect of this is to exaggerate the breadth of Eurasia considerably, and reduce the apparent gap eastward, from the eastern shores of Asia to western Europe, by about 50 degrees. This was to cause major problems for Pacific navigators from around the beginning of the 16th century, until late in the 18th century.